Tukysa (tucatinib)

P2, N=720, Recruiting, Canadian Cancer Trials Group | Trial primary completion date: Jan 2026 --> Dec 2026

P2, N=37, Recruiting, Memorial Sloan Kettering Cancer Center | Trial primary completion date: Jun 2026 --> Jul 2027

The value of HER2-targeted treatments in patients with HER2+ mCRC has been evidenced by clinical trials and meta-analyses, with strong evidence from MOUNTAINEER and DESTINY-CRC01 which supports the use of tucatinib + trastuzumab or trastuzumab deruxtecan, respectively, among this patient population. Strong evidence and clinical guidelines support the value of HER2-targeted treatment among patients with HER2+ mCRC. There is a need for increased awareness and earlier uptake of HER2 testing among patients with mCRC to broaden treatment options and optimise outcomes for this patient population.

Key 2025 findings (50 clinical trials) include: (1) confirmation of overall survival benefit with adjuvant CDK4/6 inhibitors in HR+/HER2- early breast cancer (monarchE: HR = 0.842, p = 0.0273); (2) establishment of trastuzumab deruxtecan (T-DXd) as a new standard in high-risk HER2+ early disease (DESTINY-Breast05: IDFS HR = 0.47) and first-line metastatic settings (DESTINY-Breast09: PFS HR = 0.58); (3) validation of TROP2-directed ADCs as first-line therapy for metastatic triple-negative breast cancer (ASCENT-03: PFS HR = 0.62; BEGONIA: ORR 79%); (4) paradigm shift to proactive, liquid biopsy-guided therapy switching (SERENA-6: PFS HR = 0.44); (5) updated efficacy and safety of the oral SERD imlunestrant from the EMBER-3 trial, supporting its role in ESR1-mutated advanced breast cancer and in combination with abemaciclib; (6) confirmation of long-term survival benefit for neoadjuvant carboplatin in early TNBC and new positive adjuvant data; (7) pivotal advances in HER2+ metastatic disease sequencing with tucatinib and T-DXd; (8) evidence supporting optimized adjuvant endocrine therapy in HER2+/HR+ early disease; and (9) emergence of novel agents with improved therapeutic indices, including PROTAC degraders, oral SERDs, and mutant-selective PI3K inhibitors. Unifying themes include biomarker-driven personalization, strategic treatment sequencing, management of unique toxicities, and emphasis on patient-reported outcomes. Future challenges include optimizing treatment integration, managing financial toxicity, and ensuring equitable global access.

P2, N=40, Active, not recruiting, Seagen, a wholly owned subsidiary of Pfizer | Trial completion date: Dec 2025 --> Dec 2026

P2, N=20, Recruiting, Institut Curie | Not yet recruiting --> Recruiting

P1, N=25, Active, not recruiting, Pfizer | Trial completion date: Dec 2025 --> Dec 2026 | Trial primary completion date: Dec 2025 --> Dec 2026

P2/3, N=650, Not yet recruiting, Hoffmann-La Roche

P1/2, N=20, Not yet recruiting, Institut Curie

P1, N=20, Not yet recruiting, Amsterdam UMC Stichting

P2, N=9, Active, not recruiting, Memorial Sloan Kettering Cancer Center | Recruiting --> Active, not recruiting | N=28 --> 9

Cyclin-dependent kinase 4/6 inhibitors (CDK4/6i; palbociclib, ribociclib, abemaciclib, dalpiciclib) combined with endocrine therapy (ET) were a major advance in the treatment of hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer (MBC) worldwide...However, clinical development of CDK4/6i in HER2+ MBC slowed, given the advent of highly effective tyrosine-kinase inhibitors (TKIs) (i.e., tucatinib) and antibody-drug conjugates (ADCs) (i.e., trastuzumab deruxtecan), which currently dominate the treatment armamentarium...Subsequently, the phase III PATINA trial (which included patients with 1L HR+HER2+ MBC, treated with palbociclib vs. placebo with maintenance ET+ H[P]) noted a striking PFS improvement of >15 months in the palbociclib arm, renewing interest in CDK4/6i-based treatments for HR+HER2+ MBC. Herein, we review the development of CDK4/6i in HER2+ BC, discussing current challenges and potential future directions.